This invention relates generally to an apparatus and method for treating sewage water and, more particularly, to the aeration of sewage water.
The construction of relatively large conduit systems for collecting sewage water in communities is limited due to the fact that sewage water becomes rotten in the systems. The rottening of the sewage water results from the generation of hydrosulfuric acid and other poisonous gases in the water. This rottening takes place in the sewage water between three and six hours after it has left the household if sufficient oxygen is not added to it so that natural biological reactions can take place.
The poisonous gases that are generated by the rottening of the sewage water makes it difficult to purify the water effectively in the purification plants and causes odor problems at larger pump stations. The hydrosulfuric acid is also a health hazard.
Accordingly it is important that the rottening of sewage water in conduit systems be minimized by adding oxygen thereto. Studies made by R. D. Pomeroy and J. D. Parkhurst have shown that the oxygen consumption of sewage water can be as high as 20 mg/l per hour in conduits and pump stations because of the presence of a biological coating on the conduit walls and because of the growth of active sludge in the sewage water. By adding oxygen to the water during its transport through the conduit system it is possible to considerably reduce the organic load on the purification plants and make increased capacity possible.
The best place for adding oxygen to sewage water is when it has passed the smaller local systems and has begun to be collected in the first pump stations. Generally, by then the water has been in contact with the smaller pipes in the system during a period of about 30 minutes. The oxygen reaction rate developed by Pomeroy and Parkhurst indicates that at that time the risk of oxygen deficiency (septicity) occurs, which means that oxygen addition obtains a maximum effect at that point. Further forward in the conduit system, water passes further pump stations by which the time intervals between the stations are generally about 30 minutes.
The present invention concerns a method and apparatus for aeration of sewage water in pump stations.